Adding reflection to a plane while keeping a perfect white emission
Final:



Nodes and overview:


You will need to create "fake PBR" shader by mixing Diffuse with Glossy by Fresnel.
Glossy should have set 0 Roughness and Color to pure white.
Mix them with Emission shader - again by Fresnel.





  Note:
  
  I've used black Environment color to show that Emission and Reflection
  is working, if you set it to white, like in every else node it will
  give you wanted result.